Conventionally, there is known a plasma generation device that generates electromagnetic wave plasma by emitting electromagnetic waves in a target space. For example, Japanese Unexamined Patent Application, Publication No. 2009-38025 and Japanese Unexamined Patent Application, Publication No. 2006-132518 disclose plasma generation devices of this kind.
More particularly, Japanese Unexamined Patent Application, Publication No. 2009-8025 discloses a plasma enhancement device that generates a spark discharge at a discharge gap of a spark plug and emits microwaves toward the discharge gap at the same time. In the plasma enhancement device, plasma generated by the spark discharge receives energy from microwave pulses. As a result of this, electrons in a region of the plasma are accelerated, ionization is promoted, and the plasma increases in volume.
Also, Japanese Unexamined Patent Application, Publication No. 2006-132518 discloses an ignition device of an internal combustion engine that generates plasma discharge by emitting electromagnetic waves in a combustion chamber from an electromagnetic radiator. On a top surface of a piston, an ignition electrode is provided, insulated from the piston. The ignition electrode serves a role to locally enhance electric field intensity of the electromagnetic wave in the vicinity thereof in the combustion chamber. The plasma discharge is generated in the vicinity of the ignition electrode. In the example shown in FIG. 3 of Japanese Unexamined Patent Application, Publication No. 2006-13251, a plurality of ignition electrodes are provided. In this case, it becomes possible to generate plasma discharges in a plurality of locations.